1. Field of the Invention
The present invention relates to the area of medicine known as radiation oncology which uses radiation to treat cancer and, more specifically, to a method for mounting radiation treatment blocks on a radiation treatment block mounting tray, an adjustable radiation block mounting tray and a template and method for making a form for casting a radiation treatment block.
2. Description of Related Art and Other Considerations
Radiation produced in a machine and directed towards cancer in humans and animals was found to be effective by the early 1900's. Original machines did not have apertures to control the size of the radiation beam, but later improvements in the form of blocking apertures were placed around the radiation beam to reduce the size of the emanating beam and to provide some protection to uninvolved body structures and anatomy of the patient. The ability to provide protection to uninvolved body structures is highly desirous and allows physicians to increase the radiation dose with the aim of obtaining enhanced results in the treatment of the cancer. To that end, radiation treatment blocks were developed.
Radiation treatment blocks are blocks of metal placed in the path of the radiation beam to shape the radiation beam so that the beam is applied to the prescribed area of treatment for the patient. Historically, radiation blocks were produced in standard shapes without regard to the specific anatomy of a patient. This often required that multiple blocks be utilized to shape the radiation beam to the desired field. This is labor intensive as typically the blocks are heavy. Also, because the blocks were available only in preformed geometric shapes, it also made it difficult to precisely shape the radiation beam to the anatomy of each patient.
More recent technology allows a radiation treatment block to be custom fabricated to precisely shape the radiation beam to a specific patient's anatomy. However, even with the development of custom fabricated radiation treatment blocks, problems with mounting and adjusting the blocks within the radiation beam have persisted. The present methods and apparatuses solve these problems.
Custom blocking structures, or radiation treatment blocks, must be tailored to precisely fit patients and their anatomies. Therefore, for each patient, each block is cut or configured with an aperture which is precisely shaped to “fit” the specific patient's anatomy and is placed in the path of the radiation treatment beam to provide further protection to uninvolved anatomy, thereby allowing even higher doses of radiation to be delivered to the cancer. As higher and higher doses are administered to the patient, the exact position of these blocks in the beam is of paramount importance, because even small deviations of the block aperture and, thus, the beam configuration can lead to permanent, irreversible damage to uninvolved anatomy of the patient.
There are several conventionally employed block positioning techniques and devices for shaping the radiation beam, but all have deficiencies as more fully discussed below, such as block misalignment and inaccurate positioning, the potential for radiation contamination of the treatment facility with toxic and carcinogenic heavy metals, and creating environmentally toxic waste.
A. Misalignment/Inaccuracy Problems
Currently, blocks are typically set on a clear plastic plate known as a block mounting tray or plate, which fits into the radiation treatment machine. The block is typically held in position by gravitational force when the tray is in its horizontal position with respect to the treatment machine. Typically, a radiation technologist, that is the person who administers the radiation to the patient on a day-to-day basis, places and aligns the block each day by hand. This is a tedious, time-consuming procedure, which often results in significant day-to-day variation in positioning the block, all of which are undesirable. Due to the constant handling of radiation treatment blocks by the technologist, there is a potential for the technologist to be exposed to the toxic heavy metals in the block.
An article entitled “Potential Exposure to Metal Fumes, Particulates, and Organic Vapors During Radiotherapy Shielding Block Fabrication” appearing in the September/October 1986 edition of Medical Physics identified potential hazards to block handling personnel as including: (1) bruises to hands or feet from dropped blocks, (2) inhalation of metallic dust particles and fumes, (3) ingestion of metal alloy, (4) skin absorption of metal alloy, and (5) lifting hazards posed by placing very heavy blocks into position.
When the tray is in a more vertical position and, therefore, not supported by the block mounting tray, the block will move or slide off of the tray unless the block is held onto the tray. Accordingly, various methods and devices have been used to mount the block to the tray. The most widely-used method involves the drilling of a hole in the bottom of the block and screwing it to the tray with a simple sheet metal screw. However, many technologists have difficulty in performing this task because it requires a certain degree of skill and careful positioning of the block on the tray, and the effective use of a drill and sheet metal screws. In addition, because the metals and alloys most commonly utilized to form the block are relatively soft, the screw threads in the block can easily be stripped, making it difficult to securely affix the block to the tray. The result is often that the block is poorly secured to the tray, and is loose and slightly misaligned with respect to the beam.
Efforts to correct these problems create further difficulties. When a block is misaligned but fixed to the tray, some technologists often simply compensate for the misalignment by moving the patient, who is already laying or positioned on the treatment machine, with respect to the beam. However, such movement of the patient may create an aberration in the geometry calculated for the treatment and result in a significant change in the dose of radiation delivered to the patient. Furthermore, such compensation may not be communicated to another technologist who provides subsequent treatment. As a result, uninvolved structures or radiation sensitive body parts in the patient may be over-irradiated and permanently damaged.
Other technologists, when confronted with a fixed, but misaligned block, usually elect to cancel treatment on that day and have the patient return for treatment on a subsequent day, after the tray has been dismantled and the block re-affixed to the tray. Such cancellation results in wasted time and effort for both the patient and the technologist, including lost treatment days for the patient. In addition, this subsequent effort to re-affix the block to the tray may also result in a misaligned block. Remounting the block also requires additional handling of the block, which increases the risk that the radiation technologist may be exposed to the toxic metals that are present in the block.
Another method, in an effort to improve the alignment of the block with respect to the tray, involves the milling of slots through the tray. With this method, the sheet metal screw is loosened, the block is slid with respect to the tray, and the screw is then retightened. This procedure allows the block to be adjusted in one direction, with the goal of regaining the proper alignment. Unfortunately, because such milled slots allow an adjustment in only a single direction, their use does not allow the block to be adjusted in a direction perpendicular to that of the slots. Furthermore, the milling of intersecting perpendicular slots in a tray may weaken its structural integrity and, because the blocks are relatively heavy, they can cause the tray to sag, resulting in the misalignment of the block or even fracture, possibly causing injury to the patient or attending personnel.
A less-commonly used system to affix a block to a tray involves the use of a double-sided, adhesive, foam tape. This system suffers from the alignment-of-the-tray-to-block problem described above, as well as from an inability to adjust the block once it is fixed to the tray. In addition, it is possible that a block, which can weigh as much as twenty-five pounds, could fall on a patient or a technologist, which renders this tape-fixing system a less-favored solution due to safety concerns.
B. Contamination of the Radiation Treatment Facility
In addition to the above-described problems, most blocks are formed from an alloy of toxic heavy metals, specifically lead and cadmium, both of which have known health risks. Cadmium is also known to be highly carcinogenic. The repeated handling of these blocks potentially exposes the technologists to these toxic and carcinogenic metals. Additionally, any drilling of them creates an even greater health risk in the form of fine toxic and carcinogenic dust which, without proper handling, can rapidly permeate the radiation treatment facility and, thus, create a hazardous environment for patients and personnel within the facility.
A variation of the sheet-metal-screw method described above is directed to avoid the drilling of the block and, therefore, the contamination of the radiation treatment facility. In this variation, a sheet metal screw is sunk into the alloy while it is still molten to form a properly molded hole. Once the alloy has solidified, the sheet metal screw is removed and replaced by a shorter sheet metal screw for securing the block to the tray. Although this method avoids the generation of fine, toxic dust from drilling, it still suffers from the other disadvantages of the previously-described method, that is, the metal of the block being softer than the metal of the screw creates the chance that the threads produced in the block can become stripped, which can cause misalignment of the block or result in the block falling off the tray and injuring the patient or technologist. Correction of misalignment problems is difficult and time consuming. If the threads become stripped, a new block has to be cast and/or a new hole has to be drilled. If a new hole is drilled, toxic shavings and dust are created.
C. Environmentally Toxic Waste
Another known method to affix a block to a tray is by sinking a one or more threaded rod into the molten alloy while the alloy is in the block forming mold. After the alloy has cooled a nut can be screwed onto each threaded rod protruding through a hole or slot in the tray in order to affix the block to the tray. This technique again requires an alignment of the tray to the block and can result in possible misalignment inaccuracies due to a single attachment point when one rod is used which can allow the block to shift or rotate on the tray. If more than one rod is used it creates multiple attachment points which makes it difficult to adjust the position of the block on the tray. Furthermore, after the block is no longer needed, the block is melted, whereupon each threaded rod will float to the top of the molten alloy where they can be retrieved. Retrieved threaded rods, however, are usually coated with solidified hazardous alloy or metals and are therefore, unusable. As a result, the rods must be disposed of in accordance with environmental regulations. This creates additional hazardous materials that must be disposed of at licensed disposal facilities. Proper disposal of toxic materials is both costly and time consuming for the facility staff due to the documentation required by environmental regulations. In the past, improper disposal of toxic metals into the general waste system of the local municipality has resulted in toxic pollution to the environment. As an example, many species of trees and the white-tailed ptarmigan of the Rocky Mountains have thereby been exposed to cadmium toxicity as a result of improper disposal or containment of materials containing cadmium.
D. Current Radiation Block Forming Techniques
Currently, radiation treatment blocks are typically prepared by a technologist drawing the perimetric outline of a block around a prescribed treatment area that has been drawn on an x-ray film of a patient by an oncologist. The technologist first draws the outline of the appropriate size radiation treatment block and then traces that pattern on a foam block cutting machine to cut the outline of a radiation treatment block. This procedure is difficult because the technologist has to decide on the correct perimetric outline of a block and oftentimes has no specific guidelines for making the decision. As a result, the sides of a resultant block are oftentimes not square, not properly oriented and of insufficient thickness resulting in the radiation beam spilling over the outer edge of the block. This can result in radiation being applied to uninvolved structures and patient anatomy. The template of the present invention allows a technologist to overlay a template on the marked x-ray film or vice versa. The technologist then can readily observe the appropriate perimetric outline on the template and simply trace the outline using the stylus of the foam block cutting machine. A hot wire present in the machine cuts the perimetric outline of the foam block to correspond with the perimetric outline on the template. A designated beam shaping area can also be cut within the body of the block that will shape the radiation beam for the prescribed treatment. The use of the template saves the technologist time in the preparation of a form for casting a radiation treatment block. The template optionally also provides notches on the sides and corners of the perimetric outlines of the blocks.
Tracing of the notches with the stylus of the foam block cutting machine when the perimetric outline of the block is being cut in the foam block will create notches in the block when it is cast. The notches in the block will accept the shaft of a clamping device of the present invention to assist in aligning and clamping a block to a mounting tray or plate.
E. Description of the Art
The patent literature includes a description of technology encompassing the above-described problems.
U.S. Pat. No. 5,115,139 (“Cotter patent”) discloses a slotted bracket attached to the underside of a block, through which a connecting bolt passes to run in a slot milled into a tray. The device of the Cotter patent allows the block to be adjusted in a lateral direction and to rotate the block on the tray. However, the device disclosed in the Cotter patent is not applicable to most modern blocks now commonly used, which are specifically cast to match the anatomy of a unique patient undergoing treatment. Furthermore, the device involves only a single point-of-attachment for these heavy blocks that allows for possible unintended rotation or migration of the block on the tray under the influence of gravity. The device also requires that holes be drilled into or cast into the block. If holes are drilled, the Cotter device creates toxic metal dust and particulate matter. If the holes are drilled or cast, they are prone to stripping due to the softness of the metal that is most commonly used to form the blocks.
U.S. Pat. No. 4,266,139 (“'139 patent”) describes a base plate that moves in parallel mounting rails. The device disclosed in the '139 patent allows a plate with a masking overlay to be mounted on a radiation machine. The device, however, does not allow precise multidirectional adjustment of the masking overlay. In addition, the device uses Velcro strips to attach thin metal shield plates thereto. Such a system is incompatible with most custom cast blocks in use today, which can be very heavy and would raise safety concerns if the block fell from the tray.
U.S. Pat. No. 4,472,637 (“'637 patent”) discloses a base plate that can be mounted in slots on a radiation machine. The device allows only bi-directional movement of blocking shields. The '637 patent also discloses a shield with a single attachment point which can be prone to misalignment or rotational movement of the shield on the tray resulting in inaccurate and potentially injurious treatment of the patient.
U.S. Pat. No. 5,056,128 (“'128 patent”) discloses a metal base plate and allows the magnetic mounting of radiation shielding devices. The apparatus would likely not work with the radiation treatment blocks currently in use because: (1) they are not magnetic, and (2) the size and weight of the blocks may make magnetic mounting unsafe.
U.S. Pat. No. 4,700,451 (“'451 patent”) describes a method for indexing a block to a tray. The method, however, uses screws to attach the custom cast block to the tray. This method requires that holes be drilled into the block to secure the screws. This creates toxic dust and particulate matter which exposes technologists to toxic metal. This method also creates the potential for the screws to strip out of the holes resulting in possible misalignment of the block or could result in the block falling off the tray and injuring a patient or technologist.